1. Field of the Invention
The present invention relates to a chemically amplified resist composition and, more particularly, to a monomer having a lactone group, and a polymer and a resist composition prepared using the monomer.
2. Description of the Related Art
As manufacturing processes of semiconductor devices become more complicated and as integration density of semiconductor devices increases, the need to be able to form fine patterns also increases. As an example, in semiconductor memory devices having 1-Gigabit or more storage capacity, a pattern size having a design rule of 0.2 xcexcm or less is needed. However, when a conventional photoresist material is exposed with a KrF excimer laser (248 nm wavelength), there is a limitation to forming such fine patterns. For this reason, a lithography technique using a new exposure light source, an ArF excimer laser (193 nm wavelength), has emerged.
Almost all well-known ArF resist compositions contain (meth)acryl-based polymers. Among these polymers, a methacrylate copolymer having an alicyclic protecting group, which is expressed by the formula below, has been suggested (J. Photopolym. Sci. Technol., 9(3), pp. 509 (1996)). 
This polymer has an adamantyl group, which contributes to enhancing resistance to dry etching, and a lactone group, which improves adhesiveness, in its methacrylate backbone. As a result, the resolution of the resist and the depth of focus has improved. However, resistance to dry etching is still weak, and serious line edge roughness is observed after line patterns are formed from the resist layer.
Another drawback of the polymer having the formula shown above is that the raw material used to synthesis the polymer is expensive. In particular, the manufacturing cost of a polymer having a lactone group, which is introduced to improve adhesiveness, is so high that its practical use as a resist is difficult. Therefore, there is a need for a new polymer capable of replacing costly polymers for practical use.
As an example of another conventional resist composition, a cycloolefin-maleic anhydride (COMA) alternating polymer having the following formula has been suggested (J. Photopolym. Sci. Technol., Vol. 12(4), pp. 553 (1999), and U.S. Pat. No. 5,843,624) 
In the production of copolymer, such as a COMA alternating polymer having the formula shown above, the production cost of raw materials is cheap, whereas yield of the polymer sharply decreases. In addition, the transmittance of the polymer is very low at a short wavelength region, for example at 193 nm. The synthetic polymers have in their backbone the alicyclic group, which shows prominent hydrophobicity, and as a result, adhesiveness to neighboring material layers is very poor.
To improve the resolution of resist layer, the polymer system must be charged with a polar group. In recent years, a technique of introducing a lactone group into a methacrylate monomer having an alicyclic protecting group, using the following alicyclic compounds with lactone group, has been suggested so as to enhance the resistance to dry etching (Journal of Photopolymer. Science of Technology, Vol. 13, No. 4 (2000), pp. 601-606, and Japanese Patent Publication No. P2000-26446A): 
Unfortunately, yield of the monomer having the formula shown above is so low as to cause an increase in manufacturing cost.
A feature of an embodiment of the present invention is a photosensitive monomer comprising an adhesive lactone group having both a double bond capable of forming a polymer and a photosensitive group.
Another feature of an embodiment of the present invention is a photosensitive polymer having an adhesive lactone group in its backbone and comprising a photosensitive group.
Yet another feature of an embodiment of the present invention is to provide a resist composition that can be produced at low cost with improvements in terms of dry etching resistance, adhesiveness to underlying material layers, line edge roughness of line patterns, and contrast characteristic, which are essential to realize fine patterns.
In accordance with a first embodiment of the present invention, there is provided a photosensitive monomer including a methylene butyrolactone derivative represented by the following formula: 
wherein R1 is a hydrogen atom or alkyl group, R2 is an acid-labile group, X is a hydrogen atom, or substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and Y is a substituted or unsubstitued alkyl group or alicyclic hydrocarbon group having 1 to 20 carbon atoms.
Preferably, R2 is a t-butyl, a tetrahydropyranyl, or a substituted or unsubstituted alicyclic hydrocarbon group having 6 to 20 carbon atoms.
When R2 is an alicyclic hydrocarbon group, R2 may be 1-methyl-1-cyclohexyl, 1-ethyl-1-cyclohexyl, 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1-adamantyl-1-methylethyl, 2-methyl-2-fenchyl or 2-ethyl-2-fenchyl.
In the photosensitive monomer, Y is an alicyclic hydrocarbon group and represented by the following formula: 
wherein R1, R2 and X are as defined above.
In another aspect of the first embodiment of the present invention, there is provided a photosensitive monomer comprising a methylene butyrolactone derivative represented by the following formula: 
wherein R1 is a hydrogen atom or alkyl group and R2 is an acid-labile group.
In accordance with a second embodiment of the present invention featuring a photosensitive polymer having an adhesive lactone group in its backbone and comprising a photosensitive group, there is provided a photosensitive polymer having the following formula: 
wherein R1 is a hydrogen atom or alkyl group, R2 is an acid-labile group, X is a hydrogen atom, or substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and Y is a substituted or unsubstitued alkyl group or alicyclic hydrocarbon group having 1 to 20 carbon atoms.
In accordance with another aspect of the second embodiment of the present invention, there is provided a photosensitive polymer having the following formula: 
wherein R1 and R2 are as defined above.
In accordance with still another aspect of the second embodiment of the present invention, there is provided a photosensitive polymer including (a) a monomer unit represented by the following formula: 
wherein R1 is a hydrogen atom or alkyl group, R2 is an acid-labile group, X is a hydrogen atom, or substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and Y is a substituted or unsubstitued alkyl group or alicyclic hydrocarbon group having 1 to 20 carbon atoms, and (b) at least one comonomer unit selected from the group consisting of an acrylate or methacrylate monomer unit, a maleic anhydride monomer unit and a norbornene monomer unit.
In the second embodiment of the present invention, the comonomer unit may include an acrylate or methacrylate monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl group, R4 is an acid-labile group, 0 less than m less than 1, 0 less than n less than 1 and m+n=1. Also, R2 and R4 are preferably independently t-butyl, tetrahydropyranyl, or substituted or unsubstituted alicyclic hydrocarbon group having 6 to 20 carbon atoms. Alternatively, R2 and R4 are preferably independently 1-methyl-1-cyclohexyl, 1-ethyl-1-cyclohexyl, 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1-adamantyl-1-methylethyl, 2-methyl-2-fenchyl or 2-ethyl-2-fenchyl.
Moreover, in the second embodiment of the present invention, the comonomer unit may include a maleic anhydride monomer unit, and the photosensitive polymer has the following formula: 
wherein 0 less than m less than 1, 0 less than p less than 1 and m+p=1.
Alternatively, the comonomer unit may include an acrylate or methacrylate monomer unit and a maleic anhydride monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl group, R4 is an acid-labile group, 0 less than m less than 1, 0 less than n less than 1, 0 less than p less than 1 and m+n+p=1.
Also, the comonomer unit may include a maleic anhydride monomer unit and a norbornene monomer unit, and the photosensitive polymer has the following formula: 
wherein R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having 6 to 20 carbon atoms, 0 less than m less than 1, 0 less than p less than 1, 0 less than q less than 1 and m+p+q=1.
Further, the comonomer unit may include an acrylate or methacrylate monomer unit, a maleic anhydride monomer unit and a norbornene monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl, R4 is an acid-labile group, R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having 6 to 20 carbon atoms, 0 less than m less than 1, 0 less than n less than 1, 0 less than p less than 1, 0 less than q less than 1 and m+n+p+q=1.
In accordance with a third embodiment of the present invention featuring a resist composition that can be produced at low costs with improvements in terms of dry etching resistance, adhesiveness to underlying material layers, line edge roughness of line patterns, and contrast characteristics, which are essential to realize fine patterns, there is provided a resist composition including:
(a) a photosensitive polymer comprising a product of polymerization of:
(a-1) a monomer unit represented by the following formula: 
xe2x80x83wherein R1 is a hydrogen atom or alkyl group, R2 is an acid-labile group, X is a hydrogen atom, or substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and Y is a substituted or unsubstitued alkyl group or alicyclic hydrocarbon group having 1 to 20 carbon atoms, and
(a-2) at least one comonomer unit selected from the group consisting of an acrylate or methacrylate monomer unit, a maleic anhydride monomer unit and a norbornene monomer unit, and
(b) a photoacid generator (PAG).
In the resist composition, the comonomer unit may include an acrylate or methacrylate monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl group, R4 is an acid-labile group, 0 less than m less than 1, 0 less than n less than 1 and m+n=1.
Also, the comonomer unit may include a maleic anhydride monomer unit, and the photosensitive polymer has the following formula: 
wherein 0 less than m less than 1, 0 less than p less than 1 and m+p=1.
Further, the comonomer unit may include an acrylate or methacrylate monomer unit and a maleic anhydride monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl group, R4 is an acid-labile group, 0 less than m less than 1, 0 less than n less than 1, 0 less than p less than 1 and m+n+p=1.
Also, the comonomer unit preferably include a maleic anhydride monomer unit and a norbornene monomer unit, and the photosensitive polymer has the following formula: 
wherein R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having 6 to 20 carbon atoms, 0 less than m less than 1, 0 less than p less than 1, 0 less than q less than 1 and m+p+q=1.
Further, the comonomer unit may include an acrylate or methacrylate monomer unit, a maleic anhydride monomer unit and a norbornene monomer unit, and the photosensitive polymer has the following formula: 
wherein R3 is a hydrogen atom or methyl, R4 is an acid-labile group, R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having 6 to 20 carbon atoms, 0 less than m less than 1, 0 less than n less than 1, 0 less than p less than 1, 0 less than q less than 1 and m+n+p+q=1.
In the resist composition, the photosensitive polymer preferably has a weight average molecular weight of 2,000 to 100,000.
The PAG is preferably contained in an amount of 1 to 15% by weight based on the weight of the photosensitive polymer. Preferably, the PAG includes triarylsulfonium salts, diaryliodonium salts, sulfonates or mixtures thereof. More preferably, the PAG includes triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenylionium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyldiphenyliodonium triflate, 2,6-dinitrobenzyl sulfonates, pyrogallol tris(alkylsulfonates), N-hydroxysuccinimide triflate, norbornene-dicarboximide-triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbornene-dicarboximide-nonaflate, triphenylsulfonium perfluorooctanesulfonate (PFOS), diphenyliodonium PFOS, methoxydiphenyliodonium PFOS, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide PFOS, norbornene-dicarboximide PFOS, or mixtures of these compounds.
The resist composition may further include an organic base. The organic base is preferably contained in an amount of 0.01 to 2.0% by weight based on the weight of the photosensitive polymer. Also, the organic base may include a tertiary amine compound alone or a mixture of at least two tertiary amine compounds. Preferably, the organic base includes triethylamine, triisobutylamine, triisooctylamine, triisodecylamine, diethanolamine, triethanolamine or mixtures of these compounds.
The resist composition may further include a surfactant in an amount of 30 to 200 ppm.
Also, the resist composition may further include a dissolution inhibitor in an amount of 0.1 to 50% by weight based on the weight of the photosensitive polymer.
The photosensitive monomer according to the present invention includes a lactone group having both a double bond and a photosensitive group. The photosensitive polymer according to the present invention has a lactone group in its backbone and a photosensitive group. Thus, the resist composition prepared from the photosensitive polymer according to the present invention exhibits superior adhesiveness to underlying material layers, owing to the lactone group forming the backbone of the photosensitive polymer, and can improve dry etching resistance. Therefore, use of the resist composition according to the present invention in a photolithography process exhibits superior lithography performance, so that it can be very useful in the manufacture of next generation semiconductor devices.
These and other features and aspects of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.
Korean Patent Application No. 01-9001, filed on Feb. 22, 2001, and entitled: xe2x80x9cPhotosensitive Monomer, Photosensitive Polymer and Chemically Amplified Resist Composition Comprising Lactone Group Having Acid-labile Protecting Group,xe2x80x9d is incorporated by reference herein in its entirety.